Renaming, refactoring, adding static fields, splitting lines.

Removed unneeded comments.

Changed namespace name to BatteField. It was incorrectly spelled.

Changed the name of the the Battlefield class (one and only class for
now) to Game (as this will run the game).

Extracted methods: InitializeGameField, AskUserFieldSize, GenerateMines

Renamed variables: isEndOfGame to isGameOver; sizeOfField to fieldSize;

A small optimization to the DetonateMine() method.

Introduced static fields: fieldSize, battleField

Introduced constants: emptyCellRepresentation (replaced all of these:
"-" with it)

Moved greeting "Welcome to \"Battle Field\" game." on top of the Main();

Splitted some lines into a few (for the sake of the
max-80-character-long-line rule of thumb)